Ok, so before you tell me that I am an idiot and to check the tag on the pumpkin, I got the car modified, the DEALER I bought it from had no idea if the rear end gears had been replaced. So, can I use tire height, rpm and speed? I know currently Im running between 2000 and 2200 RPM at 60MPH in 5th gear, but not sure of how to do the math here. Any suggestions ?

I'm not sure of the details, but it should be possible to jack up the back of the car, spin the rear wheels, and then compare the number of wheel rotations to the number of driveshaft rotations, then do some match to come up with a ratio.

I'm not sure of the details, but it should be possible to jack up the back of the car, spin the rear wheels, and then compare the number of wheel rotations to the number of driveshaft rotations, then do some match to come up with a ratio.

Yep. If you have to turn the driveshaft 3 3/4 times for 1 tire rotation you have 3.73's.. If you have to rotate it just over 4x you have 4.10's

I'm not sure of the details, but it should be possible to jack up the back of the car, spin the rear wheels, and then compare the number of wheel rotations to the number of driveshaft rotations, then do some match to come up with a ratio.

yep. jack up the car, put a reference mark on the driveshaft, and have a friend spin the tires ONE COMPLETE ROTATION (no more and no less). the number of times your driveshaft spins is your gear ratio. of course, it's gonna be a lil difficult to see the difference between 3.73s and 3.55s. more than one reference mark will help with this.

That's how I was taught to do it too. If you have 3.73s, the driveshaft will turn three complete revolutions and 3/4 of another revolution. If you have 3.55s, the driveshaft will turn three full revolutions and slightly more than 1/2 of a revolution.

The easiest way to make sure you turn the wheel exactly one revolution is to put the valve stem at the 12:00 position, then mark the driveshaft and a point to reference it to on the diff case. Then, when the valve stem goes around to the 12:00 position, you're done.

One other thing: IF you don't have posi, both wheels will have to be turned by two people at the exact same speed. Otherwise your results will be false.

That's how I was taught to do it too. If you have 3.73s, the driveshaft will turn three complete revolutions and 3/4 of another revolution. If you have 3.55s, the driveshaft will turn three full revolutions and slightly more than 1/2 of a revolution.

The easiest way to make sure you turn the wheel exactly one revolution is to put the valve stem at the 12:00 position, then mark the driveshaft and a point to reference it to on the diff case. Then, when the valve stem goes around to the 12:00 position, you're done.

One other thing: IF you don't have posi, both wheels will have to be turned by two people at the exact same speed. Otherwise your results will be false.

Ok, so before you tell me that I am an idiot and to check the tag on the pumpkin, I got the car modified, the DEALER I bought it from had no idea if the rear end gears had been replaced. So, can I use tire height, rpm and speed? I know currently Im running between 2000 and 2200 RPM at 60MPH in 5th gear, but not sure of how to do the math here. Any suggestions ?

Ok, so before you tell me that I am an idiot and to check the tag on the pumpkin, I got the car modified, the DEALER I bought it from had no idea if the rear end gears had been replaced. So, can I use tire height, rpm and speed? I know currently Im running between 2000 and 2200 RPM at 60MPH in 5th gear, but not sure of how to do the math here. Any suggestions ?

Thanks in advance!

Stock gears in the 2005 manual shift are 3.55's. If the gears were changed, chances are you are running an aftermarket tune. Did you get a handheld with the car? Is your speedometer off? Anyhow, I've got 4.10's and my rpms are a bit higher.

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